Transcranial Direct Current Stimulation (tDCS) with weak currents is a non-invasive, low-cost, and well tolerated technique producing lasting functional changes in the central nervous system. There is increasing evidence supporting the use of tDCS to improve stroke rehabilitation. Behavioral and therapeutic outcomes of tDCS depend on the brain areas being targeted. However, conventional approaches are limited in that they insufficiently activate the target region and/or result in unspecific stimulation throughout the entire head. To address this, High-Definition tDCS (HD-tDCS) using arrays of specifically designed electrodes has been proposed. The high-definition approach results in more focal and targeted stimulation as compared to conventional electrode montages. It allows for exceptional flexibility in designing targeted and individualized electrotherapy. When focusing on peri-lesional areas the multi-electrode high-definition approach is predicted to achieve not only more focal stimulation but importantly, also increased intensity in the peri-lesional areas with the same total currents applied to the electrodes. Thus, the high-definition approach holds promise to achieving not only safer but also stronger activation of rehabilitation targets and thus more effective rehabilitation outcomes. This project will design, prototype, and validate the first electrotherapy system optimized for stroke rehabilitation, "Rehabilitation HD-tDCS" (rHD-tDCS);moreover this system is the first to apply advanced software algorithms and existing HD-tDCS technology to leverage the presence of the lesion to guide current to precise targets in an individually optimized fashion. The main goal of this project is the focal and reliable stimulation of peri-lesional cortical targets to improve stroke rehabilitation. The efficacy of the technique will be demonstrated on improved language training in stroke patients with aphasia. Milestones for a successful Phase-1 are: 1. Automated modeling and optimization of current flows in accurate anatomical models of stroke lesions and surrounding areas. 2. Prototype of a programmable stimulation device and electrode montage optimized for targeting these stroke areas. 3. Successful rehabilitation treatment of aphasia with the rHD-tDCS device. The stimulation device and protocols developed in this project are further applicable to motor rehabilitation in stroke and other promising areas of targeted electro-therapy. PUBLIC HEALTH RELEVANCE: Electrical stimulation with small currents trough the scalp produce significant improvements in rehabilitation training, in particular the recovery of language skills after a stroke. This projects aims to developed advanced technology called Rehabilitation High-Definition transcranial Direct Current Stimulation (rHD-tDCS) which can guide therapeutic electrical currents trough multiple electrodes to brain regions involved in functional recovery while sparing the rest of the brain. This is expected to improve safety, reliability, and efficacy of stroke rehabilitation training.